1. Field of the Invention
The present invention relates to a method of personalizing an electronic module, and to an electronic circuit and a module which are designed for the implementation of the method. More particularly, the present invention relates to a method for loading, into an electronic circuit included in the module, of an identifier and of other configuration data, this module forming part of an assembly of modules placed on board an automotive vehicle and interconnected in a local network for multiplex data transmission within the vehicle.
It is currently contemplated to replace the conventional electrical wiring of an automotive vehicle by a serial data transmission bus interconnecting electronic modules for controlling actuators or for acquiring signals received from sensors in the automobile. The standardizing of such an assembly of means forms the subject of a working document referenced ISO/TC22/SC3/WG1 N398E published in June, 1989 by the International Standardization Organization (ISO) and entitled "Draft proposal for recommended practice: VAN remote controlled switch".
Various electronic modules forming part of such an assembly may have the same operating protocols and standards. This is for example the case with modules for acquiring signals delivered by a temperature sensor, which may be perfectly identical from the operational point of view, whether the temperature sensed is that of the air, the cooling water, the engine oil etc. The same is also true of modules for controlling the right and left light units, for example.
It is however necessary to personalize each module in such a way that the module can recognize, out of all the signals conveyed by the bus, those modules which are intended specifically for that module. Following a working document referenced ISO/TC22/SC3/WG1 N406E published in November, 1989 by the abovementioned body and entitled "Draft standard VAN", the signals applied to the communication bus include in the form of frames, each frame comprising, in particular, a "frame-identifier" field used to designate the particular module interrogated, a "control" field which specifies the frame type transmitted, and a data field containing the data to be transmitted.
The identifier field serves to indicate to a particular module whether the data contained in the frame are intended for that module. It is therefore necessary to personalize each module, by loading into a memory zone of the module a predetermined identifier which is tied to it so that this particular module may subsequently recognize, from the communication bus, the signal frames which it should take account of, by comparing the stored identifier with an identifier appearing at the front of each signal frame.
Following a first known method of personalizing the module, the identifier is loaded via specialized input pins provided on an integrated circuit which ensures the decoding of the identifier information received by way of the communication bus. This method exhibits two major disadvantages. Firstly, the personalizing has to be carried out relatively early in the production chain of the module, at the site of the manufacturer of the module. It follows from this that two modules, perfectly identical from an operational point of view, may have different identifiers, which complicates the management of the stocks of these modules, in regard to both manufacture and after-sales service.
The other disadvantage arises because additional pins have to be provided for loading the identifier, since it not possible to disregard the cost of these pins in large-volume manufacturing operations, which must be as inexpensive as possible, as is the case in particular in automotive electronics.
This disadvantage can be eliminated by remotely e.g. at the place of manufacture, loading the identifier into a memory internal to the integrated circuit, during the manufacture of the module. This procedure however has the disadvantage that personalizing the module during manufacture complicates the management of the stocks of modules.
The loading of the identifier could be carried out by configuring the module in programming functioning mode, by application of a particular sequence of stimuli to pins of a connector provided in the module. For reasons of security, it is however necessary that this sequence cannot be reapplied to the module during normal functioning thereof. This solution has the further disadvantage of being relatively complicated to implement, in particular due to the particular constraints which it imposes on the input/output pins of the module.